The mechanism of synaptic transmission and its function for the coding of patterned motor output is studied in the insect fligh motor system and the limb motor system with both physiological and genetic techniques. Flight Motor System: L-glutamate is found to be the most potent substance to mimic the natural transmission at the excitatory junction of the indirect flight muscle of Sarcophaga bullata. However, the mimicry is not perfect, suggesting the natural transmitter could have a similar chemical structure but would be different from L-glutamate. A further search for the natural transmitter and its competitor will be conducted. The coding mechanism of flight motor output is investigated by recording the activity of each muscle fiber and each motor neuron in the flight motor center. The input-output relationship of the flight motor center will be studied with Sarcophaga and Drosophila in anesthetic flight condition. Limb Motor System: Hk, a single-gene mutant of Drosophila melanogaster, shows genetically coded activity in the limb motor center. The generator mechanism responsible for this specific neural activity will be studied with cultured neurons differentiated in vitro. The mechanism of synaptic transmission in the neuromuscular junction of Drosophila differentiated in vitro will be studied.